Magnetic alginate microparticles for purification of alpha-amylases

Spherical magnetic alginate microparticles (25-60 microm in diameter) were prepared using the microemulsion system, with water-saturated 1-pentanol as the organic phase. The limited solubility of 1-pentanol in water enabled simple removal of the organic solvent from the prepared beads with water solution. The prepared alginate microparticles were used as magnetic affinity adsorbents for specific purification of alpha-amylases. Enzyme activity was eluted by 1.0 M maltose. alpha-Amylases from Bacillus amyloliquefaciens and porcine pancreatic acetone powder were purified 9- and 12-fold with 88 and 96% activity recovery, respectively.     

Studies on Mefenamic Acid Microparticles: Formulation, In Vitro Release, and In Situ Studies in Rats

In this study, we investigated the in vitro characteristics of mefenamic acid (MA) microparticles as well as their effects on DNA damage. MA-loaded chitosan and alginate beads were prepared by the ionotropic gelation process. Microsponges containing MA and Eudragit RS 100 were prepared by quasi-emulsion solvent diffusion method. The microparticles were characterized in terms of particle size, surface morphology, encapsulation efficiency, and in vitro release profiles. Most of the formulation variables manifested an influence on the physical characteristics of the microparticles at varying degrees. We also studied the effects of MA, MA-loaded microparticles, and three different polymers on rat brain cortex DNA damage. Our results showed that DNA damage was higher in MA-loaded Eudragit microsponges than MA-loaded biodegradable chitosan or alginate microparticles.     

Encapsulation of Sorbitan Ester-Based Organogels in Alginate Microparticles

Leaching of the internal apolar phase from the biopolymeric microparticles during storage is a great concern as it undoes the beneficial effects of encapsulation. In this paper, a novel formulation was prepared by encapsulating the sunflower oil-based organogels in alginate microparticles. Salicylic acid and metronidazole were used as the model drugs. The microparticles were prepared by double emulsion methodology. Physico-chemical characterization of the microparticles was done by microscopy, FTIR, XRD, and DSC studies. Oil leaching studies, biocompatibility, mucoadhesivity, in vitro drug release, and the antimicrobial efficiency of the microparticles were also performed. The microparticles were found to be spherical in shape. Gelation of the sunflower oil prevented leaching of the internal phase from the microparticles. Release of drugs from the microparticles followed Fickian kinetics and non-Fickian kinetics in gastric and intestinal environments, respectively. Microparticles showed good antimicrobial activity against both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria. The results suggested that the developed formulations hold promise to carry oils without leakage of the internal phase. Encapsulation of organogels within the microparticles has improved the drug entrapment efficiency and improved characteristics for controlled delivery applications.

Electronic supplementary material

The online version of this article (doi:10.1208/s12249-014-0147-2) contains supplementary material, which is available to authorized users.KEY WORDS: alginate, drug delivery, leaching, microparticles, organogels     

Preparation and Characterization of Alginate Microparticles Containing a Model Protein for Oral Administration in Gnotobiotic European Sea Bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>) Larvae

Aquaculture is the fastest growing animal production sector. However, the production of marine fish is still hampered by the high mortality rate in the first few weeks after hatching. Mortality in larvae is often caused by microbial infections. Today, the incorporation of immunostimulants into microparticles provides us new tools to enhance disease resistance in marine larviculture. In this study, we prepared alginate microparticles loaded with the model antigen fluorescein isothiocyanate conjugated-bovine serum albumin. Optimum concentrations of alginate and CaCl₂, the correct alginate viscosity and the appropriate preparatory conditions led to the creation of desirable microparticles with the correct size for oral feeding in gnotobiotic European sea bass larvae. The prepared alginate microparticles were stable in sea water and were successfully ingested by gnotobiotic sea bass larvae at day after hatching 7 without causing any negative effects. Results suggest the suitability of this drug delivery system for targeting the innate immune system of fish larvae in order to enhance disease resistance and thus reduce mortality in larviculture.     

A microfluidic approach to encapsulate living cells in uniform alginate hydrogel microparticles

A microfluidic technique is described to encapsulate living cells in alginate hydrogel microparticles generated from monodisperse double-emulsion templates. A microcapillary device is used to fabricate double emulsion templates composed of an alginate drop surrounded by a mineral oil shell. Hydrogel formation begins when the alginate drop separates from the mineral oil shell and comes into contact with Ca(2+) ions in the continuous phase. Alginate hydrogel microparticles with diameters ranging from 60 to 230 μm are obtained. 65% of the cells encapsulated in the alginate microparticles were viable after one week. The technique provides a useful means to encapsulate the living cells in monodisperse hydrogel microparticles.     

Immobilization of alliinase with a water soluble–insoluble reversible N-succinyl-chitosan for allicin production

N-Succinyl-chitosan (NSC), a pH-sensitive polymer of reversibly soluble–insoluble characteristics with pH change, was prepared by modification of the chitosan backbone with succinic anhydride and employed as carrier for alliinase immobilization. The obtained NSC is soluble at pH above 4.8 and insoluble at pH below 4.4. The characteristics of NSC were evaluated using Fourier transform IR spectrophotometer, the X-ray diffraction spectrometry and thermogravimetric analyzer. Under an optimized condition (glutaraldehyde 0.8% (v/v), 31.2 U alliinase), the enzyme immobilization yield was 75.6%. The maximum activity of NSCA was achieved at 40 °C, pH 7, while the free enzyme exhibited maximum activity at 30 °C, pH 6. The Michaelis–Menten constant of NSCA was lower than that of free alliinase, indicating higher affinity of immobilized enzyme toward its substrate. The NSCA retained 85% of its initial activity even after being recycled 5 times. The immobilized alliinase in reversibly soluble NSC is suitable to catalyze the conversion of alliin to allicin, as active ingredient of pharmaceutical compositions and food additive.     

Production of cell-enclosing hollow-core agarose microcapsules via jetting in water-immiscible liquid paraffin and formation of embryoid body-like spherical tissues from mouse ES cells enclosed within these microcapsules

We developed agarose microcapsules with a single hollow core templated by alginate microparticles using a jet-technique. We extruded an agarose aqueous solution containing suspended alginate microparticles into a coflowing stream of liquid paraffin and controlled the diameter of the agarose microparticles by changing the flow rate of the liquid paraffin. Subsequent degradation of the inner alginate microparticles using alginate lyase resulted in the hollow-core structure. We successfully obtained agarose microcapsules with 20-50 microm of agarose gel layer thickness and hollow cores ranging in diameter from ca. 50 to 450 microm. Using alginate microparticles of ca. 150 microm in diameter and enclosing feline kidney cells, we were able to create cell-enclosing agarose microcapsules with a hollow core of ca. 150 microm in diameter. The cells in these microcapsules grew much faster than those in alginate microparticles. In addition, we enclosed mouse embryonic stem cells in agarose microcapsules. The embryonic stem cells began to self-aggregate in the core just after encapsulation, and subsequently grew and formed embryoid body-like spherical tissues in the hollow core of the microcapsules. These results show that our novel microcapsule production technique and the resultant microcapsules have potential for tissue engineering, cell therapy and biopharmaceutical applications.     

蒜氨酸酶的固定化及其酶学性质研究

为了提高蒜氨酸酶的稳定性并实现酶的反复利用,研究了影响蒜氨酸酶固定化的因素及固定化蒜氨酸酶的酶学性质。蒜氨酸酶的固定化以壳聚糖微球为载体,戊二醛为交联剂,固定化的最适条件为：戊二醛浓度4%,给酶量20.2U,交联时间2h。固定化蒜氨酸酶的最适pH值7.0,最适温度35℃,米氏常数Km 7.9 mmol/L,操作稳定性比较好,连续使用10次后酶活力损失低于10%。     

A novel alliinase from onion roots. Biochemical characterization and cDNA cloning

We have purified a novel alliinase (EC 4.4.1.4) from roots of onion (Allium cepa L.). Two isoforms with alliinase activity (I and II) were separated by concanavalin A-Sepharose and had molecular masses of 52.7 (I) and 50.5 (II) kD on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 51 (I) and 57.5 (II) kD by gel filtration fast-protein liquid chromatography. Isoform I had an isoelectric point of 9.3, while isoform II had isoelectric points of 7.6, 7.9, 8.1, and 8.3. The isoforms differed in their glycosylation. Both contained xylose/fucose containing complex-type N-linked glycans, and isoform II also contained terminal mannose structures. Both isoforms had activity with S-alk(en)yl-L-cysteine sulfoxides. Unlike other allium alliinases, A. cepa root isoforms had cystine lyase activity. We cloned a gene from A. cepa root cDNA and show that it codes for A. cepa root alliinase protein. Homology to other reported allium alliinase genes is 50%. The gene coded for a protein of mass 51.2 kD, with two regions of deduced amino acid sequence identical to a 25- and a 40-amino acid region, as determined experimentally. The A. cepa root alliinase cDNA was expressed mainly in A. cepa roots. The structure and function of the alliinase gene family is discussed.     

A spectrophotometric assay for allicin,alliin, and alliinase (alliin lyase) with a chromogenic thiol: reaction of 4-mercaptopyridine with thiosulfinates

Allicin (diallylthiosulfinate) is the best known active compound of garlic. It is generated upon the interaction of the nonprotein amino acid alliin with the enzyme alliinase (alliin lyase, EC 4.4.1.4). Previously, we described a simple spectrophotometric assay for the determination of allicin and alliinase activity, based on the reaction between 2-nitro-5-thiobenzoate (NTB) and allicin. This reagent is not commercially available and must be synthesized. In this paper we describe the quantitative analysis of alliin and allicin, as well as of alliinase activity with 4-mercaptopyridine (4-MP), a commercially available chromogenic thiol. The assay is based on the reaction of 4-MP (lambda(max)=324nm) with the activated disulfide bond of thiosulfinates -S(O)-S-, forming the mixed disulfide, 4-allylmercaptothiopyridine, which has no absorbance at this region. The structure of 4-allylmercaptothiopyridine was confirmed by mass spectrometry. The method was used for the determination of alliin and allicin concentrations in their pure form as well as of alliin and total thiosulfinates concentrations in crude garlic preparations and garlic-derived products, at micromolar concentrations. The 4-MP assay is an easy, sensitive, fast, noncostly, and highly efficient throughput assay of allicin, alliin, and alliinase in garlic preparations.     

Purification and characterisation of alliinase produced by Cupriavidus necator and its application for generation of cytotoxic agent: Allicin

Allicin, an extremely active constituent of freshly crushed garlic, is produced upon reaction of alliin with the enzyme alliinase (EC 4.4.1.4). A bacterium Cupriavidus necator with the ability of alliinase production was isolated from a soil sample and was identified by morphological, biochemical and 16S rRNA sequence. Alliinase production was optimised and it was further purified to apparent homogeneity with 103-fold purification and specific activity of 209 U/mg of protein by using DEAE Cellulose and Sephadex G-100 chromatography. The enzyme is a homodimer of molecular weight 110 kDa with two subunits of molecular weight 55 kDa each. The optimum activity of the purified enzyme was found at pH 7 and the optimum temperature was 35 °C. The enzyme exhibited maximum reaction rate (V_max) at 74.65 U/mg and Michaelis–Menten constant (K_m) was determined to be 0.83 mM when alliin was used as a substrate. The cytotoxic activity of in-situ generated allicin using purified alliinase and alliin was assessed on MIA PaCa-2 cell line using MTT assay and Acridine orange–ethidium bromide staining. This approach of in-situ allicin generation suggests a novel therapeutic strategy wherein alliin and alliinase work together synergistically to produce cytotoxic agent allicin.     

Thiol‐disulfide organization in alliin lyase (alliinase) from garlic (Allium sativum)

Alliinase, an enzyme found in garlic, catalyzes the synthesis of the well-known chemically and therapeutically active compound allicin (diallyl thiosulfinate). The enzyme is a homodimeric glycoprotein that belongs to the fold-type I family of pyridoxal-5′-phosphate-dependent enzymes. There are 10 cysteine residues per alliinase monomer, eight of which form four disulfide bridges and two are free thiols. Cys368 and Cys376 form a S—S bridge located near the C-terminal and plays an important role in maintaining both the rigidity of the catalytic domain and the substrate-cofactor relative orientation. We demonstrated here that the chemical modification of allinase with the colored —SH reagent N-(4-dimethylamino-3,5-dinitrophenyl) maleimide yielded chromophore-bearing peptides and showed that the Cys220 and Cys350 thiol groups are accesible in solution. Moreover, electron paramagnetic resonance kinetic measurements using disulfide containing a stable nitroxyl biradical showed that the accessibilities of the two —SH groups in Cys220 and Cys350 differ. Neither enzyme activity nor protein structure (measured by circular dichroism) were affected by the chemical modification of the free thiols, indicating that alliinase activity does not require free —SH groups. This allowed the oriented conjugation of alliinase, via the —SH groups, with low- or high-molecular-weight molecules as we showed here. Modification of the alliinase thiols with biotin and their subsequent binding to immobilized streptavidin enabled the efficient enzymatic production of allicin.     

Preparation of alginate coated chitosan microparticles for vaccine delivery

Background  

Absorption of antigens onto chitosan microparticles via electrostatic interaction is a common and relatively mild process suitable for mucosal vaccine. In order to increase the stability of antigens and prevent an immediate desorption of antigens from chitosan carriers in gastrointestinal tract, coating onto BSA loaded chitosan microparticles with sodium alginate was performed by layer-by-layer technology to meet the requirement of mucosal vaccine.     

Purification,characterization, and crystallization of alliinase from garlic

Glycosylated dimeric alliinase (EC 4.4.1.4) was purified to homogeneity from its natural source, garlic. With 660 units/mg, the specific enzymatic activity of the pure enzyme is the highest reported to date. Based on both CD spectroscopy data and sequence-derived secondary structure prediction, the alpha-helix content of alliinase was estimated to be about 30%. Comparisons of all available amino acid sequences of alliinases revealed a common cysteine pattern of the type C-x18-19-C-x-C-x2-C-x5-C-x6-C in the N-terminal part of the sequences. This pattern is conserved in alliinases but absent in other pyridoxal 5'-phosphate-dependent enzymes. It suggests the presence of an epidermal growth factor-like domain in the three-dimensional structures of alliinases, making them unique among the various families of pyridoxal 5'-phosphate-dependent enzymes. Well-ordered three-dimensional crystals of garlic alliinase were obtained in four different forms. The best diffraction was observed with crystal form IV (space group P2(1)2(1)2(1), a=68.4, b=101.1, c=155.7 A) grown from an ammonium sulfate solution. These crystals diffract to at least 1.5 A resolution at a synchrotron source and are suitable for structure determination.     

Molecular imprint of enzyme active site by camel nanobodies: rapid and efficient approach to produce abzymes with alliinase activity

Screening of inhibitory Ab1 antibodies is a critical step for producing catalytic antibodies in the anti-idiotypic approach. However, the incompatible surface of the active site of the enzyme and the antigen-binding site of heterotetrameric conventional antibodies become the limiting step. Because camelid-derived nanobodies possess the potential to preferentially bind to the active site of enzymes due to their small size and long CDR3, we have developed a novel approach to produce antibodies with alliinase activities by exploiting the molecular mimicry of camel nanobodies. By screening the camelid-derived variable region of the heavy chain cDNA phage display library with alliinase, we obtained an inhibitory nanobody VHHA4 that recognizes the active site. Further screening with VHHA4 from the same variable domain of the heavy chain of a heavy-chain antibody library led to a higher incidence of anti-idiotypic Ab2 abzymes with alliinase activities. One of the abzymes, VHHC10, showed the highest activity that can be inhibited by Ab1 VHHA4 and alliinase competitive inhibitor penicillamine and significantly suppressed the B16 tumor cell growth in the presence of alliin in vitro. The results highlight the feasibility of producing abzymes via anti-idiotypic nanobody approach.     

The Effect of Chitosan as Internal or External Coating on the 5-ASA Release from Calcium Alginate Microparticles

The effect of chitosan as internal or external coating on the mesalamine (5-ASA) release from calcium alginate microparticles (CaAl) was studied, and a delayed release of 5-ASA system intended for colonic drug delivery was developed. The external chitosan coating was developed by immersion of wetted CaAl in chitosan solution and the internal coating by mixing 5-ASA with chitosan solution and drying before the preparation of CaAl. Both systems were coated with Acryl-EZE^® using combined fluid bed coating and immersion procedure. The results showed that in phosphate medium (pH 7.5), chitosan as 5-ASA coating promotes a quick erosion process accelerating drug release, but chitosan as external coating (CaAlCS) does not increase the T ₅₀ value compared with the microparticles without chitosan (CaAl). Chitosan as internal or external coating was not effective to avoid the quick 5-ASA release in acidic medium (pH 1.2). The presence of β-glucosidase enzymes increases significantly the 5-ASA release for CaAl, while no effect was observed with chitosan as internal or external coating. Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray data revealed that 5-ASA did not form a solid solution but was dispersed in the microparticles. The Acryl-EZE^® coating of microparticles was effective because all the formulations showed a low release, less than 15%, of 5-ASA in acid medium at pH 1.2. Significant differences in the percentage of 5-ASA released between formulations were observed in phosphate buffer at pH 6.0. In phosphate buffer at pH 7.2, all the formulations released 100% of 5-ASA.     

Polyelectrolyte microcapsules as the systems for delivery of biologically active substances

Based on the method of the layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes, sodium alginate (Alg) and poly-L-lysine (PLL), novel biodegradable microcapsules have been prepared for delivery of biological active substances (BAS). Porous spherical CaCO₃ microparticles were used as templates. The template cores were coated with several layers of oppositely charged polyelectrolytes forming shell on the core surface. The core-shell microparticles were converted into hollow microcapsules by means of core dissolution with EDTA. Mild conditions for microcapsules preparation allow to perform incorporation of various biomolecules maintaining their bioactivity. Biocompatibility and biodegradability of the polyelectrolytes give a possibility to use the microcapsules as the target delivery systems. Chymotrypsin entrapped into the microcapsules was used as a model enzyme. The immobilized enzyme retained about 86% of the activity compared to a native chymotrypsin. The resultant microcapsules were stable in acidic medium and could be easily decomposed by trypsin treatment in slightly alkaline medium. Chymotrypsin was shown to be active after its release from the microcapsules decomposed by the trypsin treatment. Thus, the microcapsules prepared by the LbL technique can be used for the development of new type of BAS delivery systems in humans and animals.     

Preparation and <Emphasis Type="Italic">In Vitro</Emphasis>/<Emphasis Type="Italic">In Vivo</Emphasis> Evaluation of Microparticle Formulations Containing Meloxicam

In this study, we have formulated chitosan-coated sodium alginate microparticles containing meloxicam (MLX) and aimed to investigate the correlation between in vitro release and in vivo absorbed percentages of meloxicam. The microparticle formulations were prepared by orifice ionic gelation method with two different sodium alginate concentrations, as 1% and 2% (w/v), in order to provide different release rates. Additionally, an oral solution containing 15 mg of meloxicam was administered as the reference solution for evaluation of in vitro/in vivo correlation (ivivc). Following in vitro characterization, plasma levels of MLX and pharmacokinetic parameters [elimination half-life (t _1/2), maximum plasma concentration (C _max), time for C _max (t _max)] after oral administration to New Zealand rabbits were determined. Area under plasma concentration–time curve (AUC_0–∞) was calculated by using trapezoidal method. A linear regression was investigated between released% (in vitro) and absorbed% (in vivo) with a model-independent deconvolution approach. As a result, increase in sodium alginate content lengthened in vitro release time and in vivo t _max value. In addition, for ivivc, linear regression equations with r ² values of 0.8563 and 0.9402 were obtained for microparticles containing 1% and 2% (w/v) sodium alginate, respectively. Lower prediction error for 2% sodium alginate formulations (7.419 ± 4.068) compared to 1% sodium alginate formulations (9.458 ± 5.106) indicated a more precise ivivc for 2% sodium alginate formulation.     

Rapidly serum-degradable hydrogel templating fabrication of spherical tissues and curved tubular structures

Development of the techniques for fabricating three‐dimensional tissues still poses significant challenges for tissue engineering. We used hydrogels obtained from phenol‐substituted amylopectin (AP‐Ph) as templates for preparing multicellular spherical tissues (MSTs) and endothelialized curved tubular structures in type I collagen gel. AP‐Ph hydrogel microparticles of diameter 200 µm and fibers of diameter 500 µm disappeared within hours of soaking in a serum‐containing medium. HeLa cells and human endothelial cells were enclosed in the microparticles and hydrogel fibers, respectively, and then embedded in Ca‐alginate microcapsules or the collagen gel. The enclosed cells were released in cavities formed by hydrogel degradation in the serum‐containing medium. The released HeLa cells in the spherical cavities grew and formed MSTs, eventually filling the cavities. The spherical tissues were easily harvested by liquefying the Ca‐alginate hydrogel microcapsule membrane by chelation using sodium citrate. The released endothelial cells grew on the tubular cavity surfaces and formed tubular structures. An endothelial cell network was formed by cell migration into the collagen gel. These results demonstrate the potential of serum‐degradable AP‐Ph hydrogels in constructing three‐dimensional tissues. Biotechnol. Bioeng. 2012; 109: 2911–2919. © 2012 Wiley Periodicals, Inc.     

Enhancement of Bioavailability of Cefpodoxime Proxetil Using Different Polymeric Microparticles

Poorly water-soluble drugs such as cefpodoxime proxetil (400 μg/ml) offer a challenging problem in drug formulation as poor solubility is generally associated with poor dissolution characteristics and thus poor oral bioavailability. According to these characteristics, preparation of cefpodoxime proxetil microparticle has been achieved using high-speed homogenization. Polymers (methylcellulose, sodium alginate, and chitosan) were precipitated on the surface of cefpodoxime proxetil using sodium citrate and calcium chloride as salting-out agents. The pure drug and the prepared microparticles with different concentrations of polymer (0.05–1.0%) were characterized in terms of solubility, drug content, particle size, thermal behavior (differential scanning calorimeter), surface morphology (scanning electron microscopy), in vitro drug release, and stability studies. The in vivo performance was assessed by pharmacokinetic study. The dissolution studies demonstrate a marked increase in the dissolution rate in comparison with pure drug. The considerable improvement in the dissolution rate of cefpodoxime proxetil from optimized microparticle was attributed to the wetting effect of polymers, altered surface morphology, and micronization of drug particles. The optimized microparticles exhibited excellent stability on storage at accelerated condition. The in vivo studies revealed that the optimized formulations provided improved pharmacokinetic parameter in rats as compared with pure drug. The particle size of drug was drastically reduced during formulation process of microparticles.